Boat Stabilization

ABSTRACT

A technique for stabilizing a boat in open water against a stationary structure is disclosed. The boat has a fender at one end comprising a resilient material, and the boat is urged against the structure to engage the resilient material with the structure. The frictional engagement in combination with the urging force is sufficient to prevent the engaged fender from slipping down the structure. In this way so long as the engagement is sustained, the boat is stabilized against the structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of United Kingdom Patent Application No. 0512097.7, filed on Jun. 14, 2005, which hereby is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to the stability of boats in open water, and particularly to their stability in active waters when delivering or receiving personnel or goods at a stationary structure. The invention has especial application in relation to offshore structures.

Offshore structures around the world's coasts are becoming commonplace, and particularly with the creation of offshore wind farms, many of these structures are relatively small. Such structures do though, require maintenance and attendance for other reasons, and for these purposes only relatively short visits are often required. Similarly, only short visits are required if all that is involved in the transfer of goods or personnel to or from the stationary structure.

SUMMARY OF THE INVENTION

In active waters a floating craft is subject to a lot of vertical movement, and this can make difficult the transfer of personnel or goods from the craft to a stationary structure. The present invention seeks to facilitate such transfer by providing a means by which the craft can be temporarily stabilized against the structure. According to the invention such a floating craft has at one end a fender with an exposed surface comprising a resilient material. The craft is urged against the structure to engage the resilient material with the structure such that the frictional engagement in combination with the urging force is sufficient to prevent the engaged fender from slipping downwards relative to the structure. So long as this engagement is sustained, the movement of personnel and goods between the craft and the structure is greatly eased.

With a craft and stationary structure engaged in the manner described above, the active water will of course continue to rise and fall. This will allow the craft to pivot in a vertical plane around the point of engagement, but it is of course important that the water level cannot approach or rise above that point. Accordingly, it is preferred that the frictional engagement between the resilient material and the stationary structure permits slippage of the fender upwards relative to the structure, while resisting downward slippage. By this means the craft preserves a horizontal or upwardly inclined attitude towards the point of engagement.

The resilient material on the fender typically comprises natural or synthetic rubber, and can of course be a combination of different materials. In a preferred embodiment the resilient material comprises a rubber sleeve around a resilient foam core. The resilient material can be secured to the fender by any suitable means, bearing in mind that whatever securement is used has to be water resistant and particularly, resistant to sea water if the system is to be used offshore.

The fender will normally present a flat surface for engagement with the structure, with an area sufficient to make firm engagement with the structure which will typically be a column or pylon projecting from the water. Such a structure will allow the resilient material to engage round a significant area so that good frictional contact can be made. In some embodiments, particularly where the structure with which engagement is to be made is known to comprise a column or pylon, the fender may present a concave surface to increase the contact area. The shape of the surface being offered can of course be matched to a particular structure if regular trips to such structure or structures are to be made. This can be of particular benefit for example, when a craft has to travel to substantially identical turbines in an offshore wind farm. In some circumstances, there could be some merit in the exposed surface on the fender being convex, for engagement for example against and between two stanchions.

The fender itself may be part of the structure of the craft, or part of an assembly for fitting to a craft. Such an assembly might even be transferable between crafts, or a range of assemblies be provided for fitting to the same craft, each assembly being particularly adapted to a form of structure against which the craft is to be stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example, with reference to the accompanying schematic drawings, in which:

FIG. 1 shows a side view of a craft in stable engagement with an offshore structure;

FIG. 2 shows an enlarged plan view of the point of contact showing the engagement between the craft ad the structure in FIG. 1;

FIG. 3 shows a view similar to that of FIG. 2 of an alternatively shaped fender;

FIG. 4 shows another view similar to that of FIG. 2 with another alternative fender configuration;

FIG. 5 is a cross-section through a fender and the resilient material mounted thereon;

FIG. 6 is a front perspective view of a catamaran embodying the invention; and

FIG. 7 is a plan view showing an assembly according to the invention fitted to the bow of a monohull craft.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a craft 2 held relative to an offshore structure by engagement of its bow against a pylon 4 of the offshore structure. The craft is shown at an inclined attitude relative to the level of the sea 6, with the bow above the stern. The bow of the boat is fitted with a fender 8 upon which is mounted a resilient material 10. The craft is continuously urged against the structure by a motor (not shown), and sustains frictional contact between the resilient material 10 and the pylon 4 to hold the bow of the boat steady relative to the pylon, enabling an individual to readily transfer to a ladder indicated at 12, or other feature attached to the pylon, from the boat.

The frictional engagement between the bow of the boat and the pylon 4 is maintained by the craft being continuously urged against the pylon. This requires the engine to be kept running, and the stern of the boat where the boat is driven, to remain in the water. It is important then, that the attitude of the boat remains either horizontal as shown, inclined upwardly towards the pylon 4 to sustain the frictional engagement between the bow and the pylon. The frictional engagement with the pylon must resist downward slippage, although upwards slippage can be tolerated. Once the inclined attitude of the boat is established, rising water under the bow and the buoyancy of the bow will lift it relative to the pylon in any event, but with the drive from the engine the engagement will be sustained at a higher, and not a lower level. The weight distribution in the boat may be arranged to ensure that the inclination cannot reach an angle at which the boat itself is at risk.

FIG. 2 shows how the frictional engagement between the bow of the boat 2 and the pylon 4 can be maintained. As can be seen, the resilient material 10 is sufficiently soft to be compressed by engagement with the pylon 4 so that the area of contact between the material 10 and the pylon extends around 25 to 40% of the circumference of the pylon. With the pylon 500 mm in diameter and a vertical depth of the resilient material of 500 mm, this will establish a contact area of around 2500 cm². We have found that with natural rubber forming the exposed surface of the resilient material, this engagement can hold the bow of a boat in stable contact with an offshore structure in most normal sea conditions, provided the boat engine can generate sufficient continuous power relative to the boat weight. Typically 4 to 5 tonnes of thrust is required to maintain a boat having a dead weight of around 28 tonnes in stable contact with a pylon. This can be provided by a motor driving either a propeller or a water jet, with the latter being preferred as a water jet driven boat can operate in shallower waters; a minimum of 0.8 m as against 1.8 m depth being needed for safe operation of a propeller driven craft.

FIGS. 3 and 4 show alternative fender arrangements in contact with a pylon or pylons of an offshore structure. FIG. 3 shows a fender presenting a concave surface to the pylon; in FIG. 4 the resilient material is on a convex surface, and makes simultaneous contact with two pylons. This can provide a little additional stability by providing some resistance to lateral movement of the craft (rotation in a horizontal plane), and also a clear indication of such lateral movement as a consequence of engagement with one of the pylons being reduced or lost.

FIG. 5 shows a cross-section through the resilient material and the fender upon which it is mounted. As can be seen, the material comprises a sleeve 14 typically of rubber, around a core 16 of resilient synthetic foam. The elastomer sleeve 14 has a wall thickness of 20 mm with nylon reinforcement. The core 16 comprises polyurethane foam of density 45 kg/mm³. The overall cross-section is oval in shape, 700 mm in height and 300 mm thick. A flat side is secured to an aluminium support beam 18. The sleeve is secured to the support beam 18 by means of adhesive, but additional straps or ties may also be used as a precaution. Such ties 20 are visible in FIG. 6 which is a front view of a catamaran in which the fender extends between hull bows spaced by around 4 m. FIG. 6 also shows evidence of engagement of the resilient material with an offshore structure, and evidence of upward movement of the resilient material relative to for example, a pylon of such a structure.

FIG. 7 shows the bow of a monohull craft, upon which an assembly embodying the invention is fitted. As can been seen, the assembly has staves 22 attached to the side of the hull, with the centre of the fender mounted on the prow 24. It will be appreciated that such an assembly can be detachable for repair and for use on other crafts. The same does of course apply to a fender or equivalent assembly mounted on a multihull craft. 

1. A method of stabilizing a floating craft against a stationary structure in which the craft has at one end a beam with an exposed surface comprising a resilient material, in which method the craft is used against the structure to engage the resilient material therewith, the frictional engagement in combination with the urging force being sufficient to prevent the engaged beam from shipping downwards relative to the structure.
 2. A method according to claim 1 wherein the frictional engagement permits slippage of the beam upwards relative to the structure.
 3. A method according to claim 2 wherein the exposed surface of the beam is adapted to facilitate said upward slippage.
 4. A method according to claim 1 wherein the resilient material comprises rubber.
 5. A method according to claim 4 wherein the resilient material comprises a rubber sleeve around a resilient foam core.
 6. A method according to any claim 1 wherein the beam is part of the craft.
 7. A method according to claim 1 wherein the beam is part of an assembly fitted to the craft.
 8. A method according to claim 1 wherein the craft has a bow and a stem, with a motor for propelling the craft from the stem, and wherein the beam is as the bow.
 9. A method according to claim 8 wherein the craft is a monohull boat.
 10. A method according to claim 8 wherein the craft is a multihull boat.
 11. A water going craft fitted with a beam having an exposed surface comprising a resilient material at an end thereof for engagement with a stationary structure, the exposed surface being adapted upon said engagement with sufficient pressure, to prevent downward slippage of the beam relative to the structure.
 12. A water going craft according to claim 11 equipped with a motor with a drive mechanism at the other end of the craft for generating said pressure.
 13. A water going craft according to claim 12 wherein the drive mechanism comprises an impeller.
 14. A water going craft according to claim 111 wherein the resilient material comprises rubber.
 15. A water going craft according to claim 14 wherein the resilient material comprises a rubber sleeve around a resilient foam.
 16. A water going craft according to claim 11 wherein the beam is part of an assembly fitted to the craft.
 17. A monohull water going craft according to claim
 11. 18. A multihull water going craft according to claim
 11. 19. An assembly for fitting to a water going craft comprising a beam having an exposed surface comprising a resilient material at an end thereof for engagement with a stationary structure, the exposed surface being adapted upon said engagement with sufficient pressure, to prevent downward slippage of the beam relative to the structure.
 20. An assembly according to claim 19 wherein the resilient material comprises rubber.
 21. An assembly according to claim 20 wherein the resilient material comprises a rubber sleeve around a resilient foam core. 